1. Field of the Invention
The invention relates to a flywheel constructed from a plurality of parts for reciprocating-piston engines, especially hand-cranked diesel engines, and to a process for making same.
2. Description of the Prior Art
Such flywheels are normally made of gray cast iron. Additional parts such as a blower ring or a magnetic segmented ring or a starter ring gear can also be joined to the actual flywheel body.
In such a flywheel, a certain degree of damping of structure-borne sound is already provided by the joint surfaces. One known reason for conduction of structure-borne sound into the flywheel is the crankshaft joined thereto. The longitudinal, torsional and bending vibrations thereof are transmitted to the flywheel and radiated therefrom as a large-area sound source. The flywheel is therefore responsible for a considerable portion of the entire engine noise.
DE A 4339421 describes a two-piece flywheel with primary and secondary masses, joined together via a torsional damping device. The structure described therein is intended merely to overcome the problem of increasing the mass moment of inertia on the primary side. Noise reduction is neither intended not achieved with this construction.
In contrast, the object of the present invention is to design the flywheel with simple means such that its noise contribution to the total engine noise is considerably reduced.
U.S. Pat. No. 1,264,642 certainly describes a riveted flywheel comprising drop-forged parts, but this does not achieve the object according to the invention, since such a flywheel behaves as a homogeneous body from the viewpoint of sound characteristics.
This object is achieved according to the invention by the features of claims 1 and 9. Advantageous embodiments are described in the dependent claims.
The multi-piece construction of the flywheel can achieve significant reduction of structure-borne sound, an essential aspect being that the parts are joined to each other under initial tension. The parts can be clamped together by bolts, rivets, deep-drawing or a few spot welds. The desired damping effect on propagation of structure-borne sound is achieved in particular in the zone of the contact surfaces of the clamped-together parts.
According to the invention, a particularly inexpensive option for making the flywheel comprises the deformation of a flat plate of sheet steel by deep-drawing, in order to obtain a shallow dish with flat bottom and rounded, shallow rim. In contrast to an embodiment of the flywheel as a cast body, such a deep-drawn part does not have to be balanced, thus permitting further cost savings.
Furthermore, it is provided according to the invention that the second part is also a deep-drawn part, which is made by deep-drawing together with the first part in one working cycle.
According to an advantageous embodiment, the two deep-drawn parts have different material thicknesses; thereby better fit of the surfaces is achieved during deep-drawing.
The second deep-drawn part can cover the first part substantially over the entire surface; alternatively, however, it can cover merely an annular section of the first deep-drawn part; both a central annular section and a peripheral annular section are suitable.
By the fact that the second deep-drawn part is nested partly or completely in a wall recess of the first part, there can be achieved a flywheel surface that is more or less closed, whereby airborne noise is abated and whereby further the joint surfaces are enlarged, thus in turn opposing the propagation of structure-borne sound.
The parts of the flywheel clamped together by individual bolted, welded or riveted points can form two or more layers, and so the flywheel is made as a kind of sandwich structure. One or more middle layers can then be made of sheet steel that is more readily deformable than the outer layer. As a result, not only is it easier to deform the layers in a shared deep-drawing process, but also the damping of structure-borne sound is improved thereby.